Photochromic materials are utilized in various fields, e.g., for displays, filters for adjusting an amount of light, devices for measuring an amount of light, recording media for photogrphic printing, paint, and the like.
Recently, photochromic materials have drawn attention in the field of light-sensitive recording media suitable for laser beam since they are expected to function as a reversible memory medium for high density recording.
When a photochromic material is used in a recording layer, recording is effected in such a manner that the recording layer in the color-disappearing state is exposed to light having a certain wavelength to convert into its color by way of shifting the absorption peak within a visible light region as shown in FIG. 2. For example, a diarylethene derivative exhibits such a coloring/color-disappearing phenomenon by the ring cleavage/ring closure reaction as shown below. ##STR1##
The diarylethene derivative exhibiting the coloring/color-disappearing phenomenon is synthesized via an intermediate, 1,2-di(2,4,5-trimethyl-3-thienyl)-1,2-dicyanoethene. The intermediate contains the following stereoisomers (cis-trans isomers): ##STR2##
It is known to produce the above photochromic material by removing the trans compound which does not contribute to the coloring/color-disappearing phenomenon, and reacting only the cis compound with an acid anhydride to prevent free rotation of bonds in the molecule. However, the fixation of free rotation and the separation of the trans compound make the production process complicated and the yield of the photochromic material is increased only with difficulty. Thus, a production cost of the material cannot be lowered.